1. Field of the Invention
The present invention generally relates to an information storage apparatus and, more particularly, to an information storage apparatus which controls an operation thereof by reducing a clock frequency during a sleep mode.
The present invention also relates to a method for controlling a spindle motor used in an information storage apparatus.
In an information storage apparatus such as a disc drive unit, a sleep mode is provided so as to reduce power consumption when there is no access by a host computer for a predetermined time period. In the sleep mode, power consumption is reduced by sequentially deactivating circuit operations. Specifically, in the sleep mode, when there is no access by the host computer for a predetermined time period, operations of circuits are sequentially stopped by stopping a system clock or reducing a frequency of the system clock (clock down). In the sleep mode, the entire operation of the system is not stopped at one time. That is, in the sleep mode, operations of circuits and an operation of a spindle motor are stopped in a predetermined order with respect to passage of time so that the system can be rapidly returned to an active stated when an access is made by a host computer.
At this time, since the spindle motor is operated at a rotational speed corresponding to a clock supplied thereto, the spindle motor is stopped or the speed of the spindle motor is reduced when the clock supplied to the spindle motor is stopped or the frequency of the clock is reduced.
In an information storage apparatus using a disc-like recording medium, if a spindle motor which rotates the disc-like recording medium is stopped, it takes a long time for the spindle motor to rotate at a speed required for recording information on the recording medium. Accordingly, it is preferable not to stop the spindle motor in the sleep mode in which a possibility of access made by the host computer is high.
2. Description of the Related Art
In an optical disc apparatus, when there is no access for a predetermined time period, the above-mentioned sleep mode is set so as to stop circuit operations or an operation of a spindle motor in order to reduce power consumption.
Japanese Laid-Open Patent Application No.7-220370 (Japanese Patent Application No.6-10059) discloses a disc apparatus which performs the above-mentioned control. In this disc apparatus, a servo circuit and a laser diode (LD) are stopped when a count value of a counter exceeds a first setting value. The counter starts a counting operation when an access request is made. Thereafter, a spindle motor is stopped when the count value of the counter exceeds a second setting value, and a frequency of an operation clock of an MPU is reduced so as to reduce power consumption.
If an operation of a disc apparatus is temporarily stopped as is in the disc apparatus of the above-mentioned patent document, a servo circuit and a laser diode are stopped first. In an optical disc such as a magneto-optical disc apparatus, if the operation of the laser diode is stopped and started again, a loading operation similar to that performed when a new magneto-optical disc is loaded must be performed.
Additionally, if a clock frequency for an MPU is reduced when the count value reaches the first setting value, a frequency of a clock for generating a drive signal supplied to the spindle motor is reduced. When the drive signal generated by the clock signal having a reduced frequency is supplied to the spindle motor, a rotational speed of the spindle motor is decreased or the spindle motor is stopped.
If the spindle motor slows down or stops, a laser beam is projected on the same spot of the optical disc. In such a condition, it is possible that data recorded on the magneto-optical disc is destroyed by the laser beam. In order to eliminate such a problem, the laser beam is required to be turned off when the rotational speed of the spindle motor is decreased or the spindle motor is stopped.
However, if the laser beam is turned off, a loading operation similar to that performed when a magneto-optical disc is loaded must be performed in a predetermined sequence when the sleep mode is canceled. Accordingly, there is a problem in that it takes a long time to return from the sleep mode to a regular operation mode.